1. Field of the Invention
The present invention relates generally to a magnetic tape cassette. In particular, it relates to a magnetic tape cassette having a sliding brake for preventing wound tape reels from accidentally rotating.
2. Background Art
There are various types of magnetic tape cassettes, for example, audio tape cassettes, video tape cassetttes, etc. In a video tape cassette, generally, there is provided a brake mechanism for preventing tape reels from accidentally rotating. This brake member is necessary to prevent difficulties, such as looseness in winding of a magnetic tape, jamming of the tape due to this looseness, or the like, both in the storage the cassette outside the player and its carrying. Particularly, a video tape cassette which is widely used is arranged such that in use a magnetic tape is exposed at the front of the cassette so that looseness in winding of the tape or the like may cause various kinds of difficulty. Accordingly, the brake has a significant role.
Although there has been proposed various brake mechanisms having a variety of structures, a brake member to which the present invention is applied is arranged such that, as shown in FIG. 1, a pair of engaging pawls 23 open from a frontal side surface of a block 21 of the brake member at a predetermined angle. The pawls 23 are made of a plastic material, for example, POM resin, or the like, and are elastic to a certain extent. That is, although the pawls 23 are fixed to the block at the fixed angle, they can bend to a certain extent. Further, as shown in FIG. 2, a brake releasing bar 14, to be described later, is selectively inserted into a recess portion 25 formed in the block 21 in its bottom surface.
The thus arranged brake member 20 is disposed on a central portion of the rear of a cassette casing 10. The side from which a magnetic tape is taken out is referred to as "front". In the portion of the cassette where the brake member 20 is disposed, there are provided a pair of partition walls 16 (FIG. 1) connected with a casing side wall 15 for restricting to a certain degree the displacement of the block 21 in the right or left direction (hereinafter referred to as the "longitudinal direction"). A pair of cylindrical choke pins 7 project outside the engaging pawls 23, respectively. A brake releasing bar insertion through-hole 9 (FIG. 2) is formed in the cassette case 10 generally beneath the block 21 and between the partition walls 16. The brake member 20 is arranged to be urged toward the front of the cassette by a coil spring 6 provided behind the brake member 20.
In each of a pair of tape reels 11 (FIG. 2) around which a magnetic tape is wound, a ratchet tooth portion 13 is formed at the outer peripheral edge of a lower flange 12 of two flanges so that each of the tape reels 11 is prevented from rotating by a selective engagement between the engaging pawl 23 and the tooth portion 13.
When the video tape cassette shown in FIG. 2 is loaded in a recording/reproducing apparatus, the brake releasing bar 14 comes into the cassette through the insertion hole 9 and the brake member 20 is displaced toward the rear of the casing (in the direction of an arrow A). This displacement causes both the engaging pawls 23 to move. As a result, the respective free end portions of the pawls 23 gradually move closer to each other by the guidance of the respective choke pins 7. Thus the pawls 23 separate from the respective tooth portions 13 to thereby allow the tape reels 11 to rotate.
In thus arranged conventional brake member 20, however, there arises a problem, which will now be described. In the assembly of the brake member 20 into the cassette casing, it is preferable to provide a gap of a certain size between the block 21 and each partition wall 16. During storage of the cassette, however, the brake member 20 may become inclined or offset in the longitudinal direction of the cassette by an amount corresponding the size of the gap by the urging force of the coil spring 6. As a result, the state of insertion of the engaging pawls 23 into the tooth portions 13 (strength of abutment therebetween) becomes unbalanced and, in an extreme case, one of the engaging pawls 23 will not engage with the associated tooth portion 13. Further, in the case where the size of the gap is selected to be larger, the positions of the respective forward portions of the engaging pawls 23 are not well defined so that in a brake-released state there has been a risk of occurrence of undesirable contact between any one of the engaging pawls 23 with the associated tooth portion 13. Specifically, in a cassette which is reduced in size and weight, it is necessary to reduce the amount of insertion of the respective engaging pawls 23 into the tooth portions 13 and therefore the foregoing problem has been further intensified.